In recent years, development of square lithium secondary batteries of high energy density has proceeded as a power source for electric automobiles and the like. A square lithium ion secondary battery has an electrode group having a positive electrode and a negative electrode with a separator interposed therebetween. The electrode group is soaked with an electrolyte and housed within a battery case. Generally, the battery case is formed with an injection opening for injecting an electrolyte. The injection opening is sealed by a sealing cap after injection of the electrolyte, so that the battery case may tightly be sealed.
Patent Literature 1 discloses a sealed type battery. The structure described in Patent Literature 1 is formed as follows. A sealing cap having a pressure sensitive adhesive tape bonded to the lower surface of the sealing cap is fitted in a concave portion of an injection opening, whereby the upper surface of the concave portion of the injection opening and the bottom of the sealing cap are bonded by the pressure sensitive adhesive tape. The peripheral edge of the sealing cap is joined, by laser welding, to the battery case at the peripheral edge of the concave portion of the injection opening with the sealing cap secured temporarily.